Pellet impact drilling apparatus



Jan. 13, 1959 s, w s 2,868,509

PELLET IMPACT DRILLING APPARATUS 2 Sheets-Sheet l 7 6g atflbornes philip $l0 Luic1 rn-b ZmOVZOLOI Filed June 7, 1956 Jan. 13, 1959 P. s. WILLIAMS PELLET IMPACT DRILLING APPARATUS Filed June 7, 1956 t 2 Sheets-Sheet 2 7 abtov'oegs PELLET IMPACT DRILLING APPARATUS Philip S. Williams, Tulsa, hla., assignor, by mesne assignments, to Jersey Production Research Company Application June 7, 1956, Serial No. d9,939

7 Claims. (Cl. 255-61) This invention concerns a novel method and apparatus for drilling bore holes in the earth, and particularly for drilling petroleum Wells. The drilling method of this invention employs novel principles to secure the circulation of solid pellets in a bore hole so as to forcefully impinge on the bottom of the hole. The impact of the pellets provides percussive forces, pulverizing the formation being drilled. Circulation is maintained by a particular arrangement of apparatus permitting the propulsion and recirculation of pellets in a stream of fluid. This method, and the apparatus embodying the method, provide a unique and desirable drilling technique.

The present invention is particularly adapted to overcome some of the disadvantages of conventional rotary drilling to supply certain advantageous features heretofore unobtainable in known drilling procedures. This patent application is a continuation-in-part of Ser. No. 268,873, now abandoned, filed January 29, 1953, in the name of Philip S. Williams and entitled Pellet Impact Drilling Method and Apparatus.

In accordance with this invention, drilling action is secured by impinging hard dense pellets on the bottom of a bore hole, propelled by a high velocity fluid jet. The action of these pellets, carried by the high velocity jet, is somewhat similar to that of sand blasting. While there is some doubt as to the complete mechanism of the drilling, it appears that the action is primarily that of surface pulverization caused by the forceful and multitudinous impingement of the solid pellets against the earth formation encountered. Frictional wear and fluid erosion also contribute to the drilling action which occurs; but these appears to be relatively unimportant factors in comparison with the impact phenomenon.

The apparatus required to employ this drilling procedure is fundamentally simple in nature. Tubing connected to fluid pumps at the surface of the earth is extended downwardly into a bore hole for connection to a jet nozzle assembly. As will become apparent, the req uisite properties of the tubing are considerably less stringent in nature than those controlling the selection of tubing in rotary drilling. Thus it is not necessary that the tubing be rotated under high torque, nor that the tubing contribute any weight to the jet nozzle assembly. Consequently for many applications it is practical to use a flexible hose, and in any case lighter weight tubing may be employed than that employed in rotary drilling.

The fluid which is employed as a propulsive and recirculating agent forthe pellets may be selected from a wide range of gases or liquids. It is not necessary that the fluid possess the ability to lubricate a drill bit or to affect the cutting action of a drill bit; consequently a reasonable flexibility exists in selecting the type of fluid to be employed. In general, any of the conventional drilling muds- -e. g., oil base muds and water-base muds-having specific gravities up to 2 to 2.5 or more may be used. Furthermore, the mods may include any of the conventional weighting agents, thickening agents, stabilizing agents, viscosity agents and the like. it should be noted, however, that ordinary water has been found to be especially effective in the practice of the invention.

it should be emphasized at this point that it is generally desirable and an important requirement of the present drilling procedure to employ a drilling fluid that has a low density as compared to the density of the pellets employed. While gaseous fluids have thus far been somewhat less effective than liquids for the present invention, it is contemplated that they are particularly applicable in some situations such as shallow hole drilling. Air, steam, the light hydrocarbon gases, exhaust gases from power plants and internal combustion engines, inert gases, and other vaporizable materials may be employed as gaseous fluids.

The drilling fluid is pumped from the surface of the earth through the above tubing to a jet nozzle assembly. The jet nozzle is so designed as to convert the available pumping pressure to the form of velocity energy. Thus a substantial pressure drop is imposed on the fluid in passing through the jet nozzle so as to cause the fluid to be ejected as a high velocity fluid jet. In this connection, when employing a liquid as the drilling fluid, it is generally preferred that the nozzle impose a pressure drop of more than about pounds per square inch on the fluid.

The fluid jet referred to is positioned adjacent the bottom of the bore hole at a spaced distance above the bottom. Pellets of a suitable character are directed into the fluid jet so as to be entrained therein. These pellets are then borne by the jet so as to forcibly impinge against the bottom of the bore hole and thereby fracture and pulverize the formation.

The pellets to be employed must have certain critical characteristics. For example, it has been found that the drilling action obtainable from the impact of pellets is largely controlled by the size of the pellets employed. Thus, in the case of extremely small pellets, relatively little drilling action can be obtained; and drilling fluid flow rates must be maintained at undesirably low values in order to prevent the pellets from washing over or out of the drill hole. Conversely, extremely large pellets are also undesirable in that excessively large drilling fluid flow rates are required to suspend such pellets within the bore hole. In short, while it is generally desirable to employ the largest pellet which is consistent with the size of the hole, the pellet passageway within the drilling bit and other operating conditions, it has been established that the pellet diameter should not exceed about 1 inch and should not be less than about A; inch. Furthermore, it is also desirable to maintain the'size of the pellets in any given operation as substantially uniform as is possible. -t is further preferred that the pellets have a minimum diameter of about inch, since pellets of this size and larger provide disproportionately greater drilling rates than pellets which are up to about inch diameter.

As stated earlier, the pellets to be employed must possess a high density relative to the density of the drilling fluid, since the drilling action depends upon the kinetic energy of the pellets which in turn is proportional to their density. In this connection, it has been established that pellets fabricated from steel, steel alloys and the like have been generally found to possess a substantially unique combination of physical characteristics for the practice of the invention.

In cases where a liquid drilling fluid is employed, it is considered that the pellets should have a density relative to the drilling liquid of between 3 to l and 10 to 1, with steel pellets having a specific gravity of about 7 to 8 being unusually effective and desirable'for water and conventional drilling muds. It will be: recognized that it is necessary for the pellets to also possess a greater i density than the earth formations or other substances through which a drilling operation of the present type is performed. Otherwise, the pellets tend to be washed out of a bore hole along with the drill cuttings. It is important and necessary, then, that the pellets possess a greater density than either the drilling fluid or the drill cuttings in order that satisfactory and practical separation of the pellets from the fluid and the cuttings may be obtained. Expressed otherwise, it is necessary that the pellets possess a density sufficiently large to enable them to settle out of the stream of drilling fluid which carries the drill cuttings away from the bottom of the bore hole and up to the earths surface. It is contemplated that the pellets generally should have a density of at least about twice that of the formation to be drilled through in order to attain the most effective results.

The configuration and surface characteristics of the pellets are also critical factors in the present invention. It is important, for example, that the pellets be substantially spherical in nature and that they possess a smooth non-abrasive surface. The non-abrasive characteristic is necessary so as to limit or otherwise avoid wear of the jet nozzle assembly through which the pellets are ejected and circulated. The repeated, high velocity passage of the pelletsthrough the jet nozzle of the assem' bly would otherwise cause impractical wear of the nozzle in the event the pellets were abrasive. The same considerations control the configuration of the pellets since sharp corners or edges of any character would cause undue wear of the nozzles.

A further reason requiring that the pellets be spherical and essentially smooth lies in the fact that the very considerable kinetic energy possessed by the pellets would cause rapid pulverization of the pellets upon contact with the formation to be drilled. It is fundamental in the present invention that a spherical body possesses the best resistance to fracture due to impact; and no other shap possesses the desirable mechanical strength of a sphere in the present instance.

The critical requirements of the pellets to be employed may be emphasized from a somewhat different viewpoint. In order to secure an effective impact-pul verization effect, pellets entrained in a high velocity fluid jet must separate readily from the fluid so as to depart from fluid circulation paths and so as to overcome any fluid cushioning effect. Again, in the circulation system employed in this invention, rapid settling of pellets from upflowing fluid is required. These factors may be referred to as the separation characteristics of the pellets in the fluid employed. The separation characteristics of the pellets in large part depend upon the properties of the pellets which have been emphasized; size, density, smooth surface, and spherical configuration.

Inasmuch as the separation characteristics of the pellets depend in part upon the drilling fluid employed, the drilling fluid is preferably a low viscosity, low density fluid consistent with other requirements of the fluid. Practically the pellets must have a density substantially greater than the fluid employed. Thus, as mentioned earlier, the pellets should have a density about 3 to times the density of a liquid. Furthermore, the pellets should have a density greater than the density of the material or materials being drilled. In this connection, it is Well known in the art that subterranean rock formations and the like generally possess specific gravities as high as about 2.8, thereby making it necessary for the pellets to possess a specific gravity greater than this figure. In general, it is necessary that the pellets therefore possess a specific gravity of at least about 5 and preferably 7 or more. As mentioned earlier, steel, steel alloys and the like are especially preferred and effective for the purposes of the invention and possess specific gravities of about 7 to 8.

In stating that steel, steel alloys and the like are pre- 4 ferred for the purposes of the invention, it should be noted that the term steel is herein employed in its broadest sense. Thus, steel has elsewhere been defined as an alloy of iron and iron carbide-alone or in admixture with other alloying agents such as chromium, cobalt, nickel, tungsten, tungsten carbide, molybdenum, etc.

Due to the impact resistance required of the pellets, hardness and toughness are essential properties for the pellets to possess, and brittle materials cannot be employed. For example, finished ball bearings have been found to be impractical for use in this invention although ball bearing blanks obtained prior to surface hardening are satisfactory. It follows, then, that steels, steel alloys, iron and the like of a more brittle character are less preferred in the practice of this invention.

Due to their high density, tungsten carbide alloys of the less brittle character are attractive for use in the pellets of this invention. Thus, alloys of this character-or other dense metals or materialsmay be employed as a core material, surfaced by ferrous alloys having the required toughness. It is apparent, then, that relatively brittle materials possessing attractive weight characteristics may be used in some instances, provided such materials are protected by a protective coating in the form of a relatively tougher and impact-resistant substance.

It will be recognized that a number of techniques and apparatus may be utilized for jetting and impacting a plurality of pellets of the types described in a drilling operation. For example, it is contemplated that mechanical means may be provided in the bottom of a bore hole for mechanically lifting one or more pellets from the bottom of a bore hole and thereafter mechanically propelling the pellets against the hole bottom in order to fracture the underlying formation. It is, however, a particular characteristic of this invention to entrain the pelletsin a fluid jet and to direct the jet and the entrained pellets against the bottom of a bore hole. Recirculation of the pellets for re-entrainment in the fluid jet is also a particular feature of the invention.

To obtain the desired recirculation of pellets in the fluid jet of the present invention, the lower portion of the jet nozzle assembly is constructed to have a diameter so as to fill the major portion of the area of the bore hole. Fluid ejected from the nozzle must therefore pass upwardly in the restricted annular space between the jet nozzle assembly and the bore hole at a relatively high fluid velocity. At some point above the jet nozzle assembly an open sleeve is positioned of a nature to permit the pellets to settle therein. By the nature of this construction asubstantially greater area for fluid flow exists in the bore hole above the sleeve referred to. Consequently, pellets carried upwardly by the high velocity confined fluid stream of drilling fluid will be brought to an area where the rate of flow of drilling fluid is sharply reduced. Dependent upon the separation characteristics of the pellets as herein defined, the pellets will then settle from the drilling fluid to drop into the sleeve referred to. This sleeve is constructed to communicate with the jet nozzle so as to permit the pellets to be re-entrained in the jet nozzle.

This recirculation is effective in large part by the difference in volume rate of flow existing above and below the sleeve element referred to. Below the lip of the sleeve element, the volume rate of flow in the bore hole annulus constitutes all fluid from the surface pump plus fluid recycled through the sleeve. Above the lip of the sleeve element, the volume rate of flow in the bore hole annulus constitutes only that due to the pump. Incremental settling of pellets therefore is accelerated further. The differential volume rate of flow referred to effectively results from an aspiratory effect which furthers the efficient recirculation of pellets.

As generally identified therefore, the drilling technique of this invention depends upon the forceful impingement of pellets of a particular character against the earth forsesame I'n'atiori to be drilled. Pellets rebounding from the earth formation are carried by fluid flow upwardly and outwardly through a restricted annular space between the bore hole and the drilling apparatus. At an upper portion of the jet nozzle assembly the fluid flow velocity is cut down so as to permit the pellets to settle into a sleeve arrangement which redirects the pellets to the fluid jet employed.

The use of a jet-type pump has been found to be uniquely advantageous in carrying out and attaining the objectives of the invention. Jet pumps, as such, are well known in the art and utilize a primary jet nozzle and a secondary nozzle or throat in combination. A stream of fluid is jetted from the primary nozzle through the secondary nozzle, and additional fluid or a mixture of fluids and solids is educted or aspirated into the secondary nozzle by the action of the jet stream. The combined fluid from the primary nozzle and the fluid'eductedinto the secondary nozzle are ejected from the secondary nozzle.

In adapting the jet pump to the present invention, the primary nozzle of such a pump is secured or otherwise positioned within the lower end of a string of well pipe. The secondary nozzle is then positioned around and somewhat below the discharge point of the primary nozzle, and

the entrance into the secondary nozzle is made large enough to provide for the entry or eduction of spherical pellets into the secondary nozzle.

A stream of drilling fluid is forced down the string of well pipe and subjected to a pressure drop across the primary nozzle whereby a high velocity stream of the fluid is directed from this nozzle into the secondary nozzle. Since the entire jet pump assembly is disposed in the bot.- tom of a bore hole, and since the entire assembly is submerged in drilling fluid, at least a portion of the drilling fluid at the bottom of the bore hole is recirculated through the secondary nozzle. Pellets of the type described earlier hereinbefore, are provided at the bottom of the bore hole and are recirculated through the secondary nozzle in conjunction with the recirculating portion of the drilling fluid.

impact of the drilling fluid and pellets from the secondary nozzle against the formation underlying the bore hole causes fracture of the formation into relatively small particles. These particles are carried upwardly by the drilling fluid into the annular space between the well pipe and the wall of the bore hole and are then washed entirely out of the hole. Meanwhile, the pellets, by virtue of their greater density (relative to the drilling fluid and the formation cuttings) are settled out of the rising mixture of fluid, cuttings and pellets and are recirculated and re-aspirated by the jet pump.

Necessarily, certain features should be observed in the use of a jet pump in the present invention in order to obtain useful and practical results. Thus, it is essential that the flow rate of the drilling fluid be sufficient throughout the system to provide an lip-flowing fluid stream in the annular space between the well pipe and the bore hole which is sufficient to lift cuttings from the hole but not the pellets. Generally speaking, liquid velocities in the annular space must be at least about 100 feet per minute and should not exceed about 200 to 250 feet per minute. It will be apparent that functionally equivalent velocities should be employed for gases.

In addition to observing the fluid flow rates just stated, it is also essential that the pellets meet the various requirements as to size, shape, density, toughness, etc. and other properties which have been enumerated and discussed earlier in this description. Insofar as the number of pellets is concerned, it has been observed that wide ranges of pellet populations may be employed. It has further been observed, however, that each drilling system is generally characterized by possessing what may be termed as a saturation pellet charge with which maximum drilling rates are obtainable. Thus, it has been observed that in any given drilling system, an increase in drilling rate gen erally occurs with an increasing number of pellets until a so-called saturation charge is reached. Maximum drilling rates are obtained when a saturation charge is reached; and these rates may be maintained with pellet charges up to about 2 /2 times the size of the saturation charge.

Insofar as the jet pump itself is concerned, it has been ascertained that certain design characteristics provide uniquely advantageous drilling conditions. For example, it has been established that pellets having a diameter about /2 the internal diameter of the secondary nozzle produce maximum drilling efliciencyyfurthermore, that the diameter of the pellets should generally be about 0.28 to 0.43 (and preferably about 0.38) times the internal diameter of the secondary nozzle in order to avoid jamming of the nozzle. It has also been determined that larger size pellets (e. g. to are about 8 times as eflicient as smaller (up to about A) pellets in rate of rock removal.

Improved drilling rates are also obtained with increasing secondary nozzle lengths up to the point where the length of the nozzle is equivalent to about 10 nozzle internal diameters. value, substantially constant drilling rates are obtained up to lengths of about 20 to 25 nozzle diameters. Expressed otherwise, it has been found that a discontinuity exists in the relationship between drilling rate and the length of the secondary nozzle, when the nozzle length is equal to 10 nozzle diameters. The drilling rate drops off sharply at nozzle lengths less than this value.

It has further been ascertained that the discharge end of the secondary nozzle should preferably be maintained above hole bottom about 2.4 to 3.8 internal secondary nozzle diameters if best drilling rates are to be attained. This spacing of the secondary nozzle from the hole bottom may be readily realized by the use of feet or other suitable extension members which are secured to the jet pump and extend down the secondary nozzle. These feet or extensions may conveniently be provided with.

cutting surfaces in the form of conventional cutting elements in order to further assist the drilling operation. At this point, it is well to note that it is preferred to rotate the entire well pipe and jet pump assembly slowly within a bore hole in order to prevent seizure or binding of the overall assembly within the hole. This slow rotation of the assembly therefore makes it attractive, although not necessary, to provide and use cutting elements on the extension members.

The principles of this invention may be embodied in a wide variety of drilling apparatus. The attached drawings show representative and preferred assemblies of apparatus including the features of this invention. In these drawings:

Figure 1 illustrates in cross-section, elevational detail, a jet nozzle assembly of the simplest character to provide effective pellet impact drilling;

Figure 2 is a cross-sectional view of Figure 1 taken through the line 22 to better illustrate the apparatus configuration;

Figure 3 is a cross-sectional elevational view of a different embodiment of the invention utilizing a plurality of fluid jets in conjunction with a centrally disposed pellet recirculation channel;

Figure 4 is a cross-sectional view of Figure 3 along line 4-4;

Figure 5 illustrates a desirable modification of the invention in cross-sectional elevational detail showing a suitable stand-off arrangement to maintain the pellet jet at the proper distance from the bottom of the bore hole;

Figure 6 showns a cross-sectional view of the apparatus of Figure 5 along the line 6-6;

Figure 7 illustrates a modification of the apparatusof Figure 5 in which the jet nozzle is maintained at an inclination so as to direct fluid and entrained pellets toward For nozzle lengths in excess of this I satisfactory ll-ow rate.

assesses the side of the bore hole opposite to the standoflf arrangement. g

Referring first to Figure 1,..the impact pellet, drilling apparatus of this invention is illustrated in drilling posi tion adjacent the bottom of a bore hole 1 which has been drilled by the apparatus. The drill is suspended on a tubular support member 2 which may, if desired, be of the nature of drill pipe conventionally used in rotary drilling operations.

The drill illustrated in Figure l essentially comprises two elements. An inner nozzle clement L is provided which may be a continuation of the drill pipe 2 but which terminates at its lower end in a jet nozzle 4. The jet nozzle assembly is therefore of a jet pump character to result in the propulsion of a fiuid jet at its lower end when drilling iiuidis pumped through the drill pipe at a The single fluid jet provided in this apparatus is directed vertically downward along theccntral axis of the bore hole.

Encircling the jet nozzle assembly 3 is a sleeve 5. This sleeve is formed and positioned so as to extend upwardly from a level below the terrninatio-n of the jet nozzle t to a level above the jet nozzle. As illustrated, the sleeve has an external diameter substantially greater than the diameter of the drill pipe 2. This configuration is employed to provide an annular channel encircling the jet nozzle assembly having a substantially smaller crosssectional area than provided above the sleeve. The upper termination of the inner portion of the sleeve may be flared upwardly and outwardly so as to provide a hopper for the collection of pellets settling from the fluid above the sleeve.

Suitable structural members such as webs, or the like, may be employed to connect the sleeve 5 in fixed relation to the jet nozzle 3. To minimize problems of wear caused by impingement of the circulated pellets through the annular channel between sleeve 5 and nozzle 3, it is desirabl to employ longitudinal ribs which extend vertically through this annular channel. Ribs of this character are identified by numeral 8, extending from the upper termination of sleeve 5 to a point adjacent and above the jet nozzle The vertically positioned ribs 8 are thus only exposedto direct impingement of the pellets on the upper edge of each rib where the pellets have a relatively low velocity.

The operation of the drill of Figure 1 may now be appreciated. Assuming that a drill hole has been initiated in the earth for at least a short distance, the aparatus of this invention may be placed in operation by lowering the drill to a position spaced from the bottom of the hole in the manner shown. Drilling mud or any desired fluid of the character described is then pumped through the drill pipe so as to be ejected from the jet nozzle 4 in the form of a high velocity constricted jet. This fluid jet passes through the elongated constricted passage h provided in sleeve 5 and impinges on the bot tom of the bore hole. The fluid will then flow outwardly and upwardly into the bore hole so as to be returned to the surface of the earth for recirculation through the drill pipe and through the jet. A multitude of solid, heavy density pellets may then be dropped into the an nular space between the bore hole and drill pipe at the surface of the earth or into the drill stem itself, nozzle size permitting. These pellets will drop downwardly so to be entrained in and ejected by the fluid jet from nozzle {1. Traveling with the energy provided by the jet of drilling fluid, the pellets will be forcefully directed against the bottom of the bore hole. The velocity of the drilling fluid will then carry the pellets outwardly and upwardly along the bottom and wall of the bore hole to a point somewhat above the upper termination of the sleeve 5. This movement of the pellets will occur by virtue of the fact that the sleeve 5 has a diameter which fills the major portion of the cross-sectional diameter of the bore hole. Consequently, a relatively confined annular channel is provided for the drilling mud between the sleeve 5 and the bore hole 1. The drilling mud thus travels upwardly adjacent the sleeve at a relatively high linear velocity, serving to maintain. entraihrnent of the pellets. However, above the upper termination of the sleeve 5 a substantially greater cross-sectional flow area is provided for the drilling mud. Consequently, the linear velocity of the drilling mud will drop sharply somewhat above the upper edge of the sleeve. This action will slow the drilling rnu'd sufficiently to permit separation of the pellets. These pellets will therefore settle out of the mud stream, dropping into the upwardly flared termination of the sleeve 5. Under the force of gravity, and in part due to the aspirating effect of the nozzle d, the pellets will drop downwardly in the annular space between the nozzle element 3 and the sleeve 5 to be caught by the jet of drilling mud and ejected by the nozzle to be again impinged against the bottom of the bore hole.

it will be noted that the sleeve 5 extends below the nozzle to provide an elongated passage or nozzle 9 having a greater diameter than that of nozzle i. Nozzle 4 may he referred to as a primary nozzle while nozzle 9, provided by sleeve 5, may be referred to as a secondary nozzle. The function of the primary nozzle, as described, is to convert a substantial portion of the pump ing pressure applied to the drilling fluid to velocity energy. The primary nozzle thus serves to provide a high velocity, constricted and directed, liuid jet. The secondary nozzle concentric with, but below t-e primary nozzle serves to entrain pellets in the fluid jet and to accelerate and direct the jetted pellets. The secondary nozzle must have a greater diameter than the primary nozzle to achieve this effect since a greater volume of material (iiuid plus pellets) must flow through the secondary nozzle. Again the greater diameter of the secondary nozzle provides an aspiratory elrect contributing to the effective entrainment of the pellets in the fluid jet. Suificient clearance must, of course, be provided between the primary nozzle and the upper open end of the secondary nozzle to permit the entrance of pellets into the secondary nozzle. Also, of course the internal diameter of the secondary nozzle must be sufficiently great to accommodate the pellets.

As heretofore described, it has been stated that the tubular support member for the drill may constitute a conventional drill string. It should be observed, however, that the present invention is particularly adapted for drilling with casing. Consequently, conventional casing of a diameter somewhat less than the normal gauge of the hole drilled by the apparatus described may be employed as a tubular support for the drill. In this case a smaller diarneter tubing, less than casing diameter, is run above the drill for a limited distance to provide the necessary settling zone for pellets. This small diameter tubing then joins to conventional casing tubing 11 through a reducing coupling as illustrated in Figure 1.

The practicality of drilling with casing in this inanner depends part upon the extensive life of the drill of this invention. Wear of the necessary nozzles may be minimized and tolerated by proper design, while pellets can be replaced as required when worn.

As the drill of Figure 1 has been described, no rotation of the drill is required. Rotation is optional although a slow rotation may be maintained to insure straight hole drilling in the eventuality the jet nozzles are not precisely directed to cut a symmetrical drilling pattern.

lowever, a valuable feature of the invention can be obtained by inclining the drill somewhat from the vertical, and normally rotating the drill at a constant rate. The drill illustrated in Figure 1 may be hired to the drill'pipe so that the axis of the drill has a substantial angle, for example, about 30, with respect to the axis of the drill ipe. Use-of an inclined nozzle in this manner is particularly illustrated in Figure 7. By constant rotation of the drill in this case, a straight hole will still be obtained but a greater diameter hole may be achieved. Again directed drilling may be obtained as desired, by employing a non-uniform rate of rotation or by stopping rotation of the drill for a period of time.

This embodiment of the invention is a particular feature as regards well completion practice. By maintaining the drill of Figure 1 at the same drilling horizon while the drill is rotated and directed at an angle to the aXis of the bore hole, a bore hole of substaiiial size may be obtained. In completing a well by this technique, a large surface of the oil producing formation may be exposed. For this purpose, the drill of Figure 1 may be inclined to the support member at an angel approaching 90.

A desirable modification of the apparatus is also obtained by fixing the drill to the drill pipe by a cranl: arm so as to maintain the drill parallel to the axis of the bore hole, but displaced therefrom a distance less /6 the cutting diameter of the drill. in this case rotation of the drill again permits the drilling of a hole of greater diameter than that normally obtained. This modification of the invention is in Figure 5.

It will be apparent that replacement of the pellets may be required during the conduct of drilling opera tions. Thus, as the pellets become worn with continued use or if they are fractured or otherwise reduced in size, eventually they will be carried upwardly with the drilling mud to the surface of the earth and will be lost from the circulation system described. When this occurs, the corresponding drop in drilling rate observed at the surface of the earth will indicate necessity for adding additional pellets which may simply be dropped into the bore hole or the drill string.

A somewhat different embodiment of the invention is illustrated in Figure 3. In this figure, the bore hole is again designated by numeral 1, and a drill string is similarly indicated by numeral 2. In place of the single jet nozzle employed in the apparatus of Figure l, a plurality of jet nozzles are employed in the apparatus of Figure 3. As will be seen, any desired number of nozzles may be used. Thus, for example, from about three to ten nozzles may be employed Each of the nozzle assemblies consists of a vertically extending conduit 13 terminating in a nozzle .15 which is directed inwardly toward the axis of the bore hole. The nozzle elements are spaced about the axis of the bore hole so as to encircle a central channel 16. The central channel 161, however, is sealed from the inner portion of the drill string 2, as by means of the sealing element or plug 17. Thus, fluid pumped downwardly through the drill string 2 cannot obtain access to the inner channel 16, but is forced in a plurality of constricted streams through the nozzle elements 1.3 to be ejected through the nozzle tips l5. At the upper portion of the apparatus, a settling. trap is provided which consists of a sleeve element 18 sealed at its lower end to provide a cupshaped chamber communicating with the inner must channel 16, through conduits 15.

It will be observed that the operation of the apparatus ofFigure 3 is similar to that of Figure 1. Drilling mud pumped downwardly through the drill string will be forced through the plurality of nozzle tips so as to be directed downwardly and inwardly from each nozzle substantially towards the axis of the bore hole at a point spaced somewhat below the nozzles. This action will provide a concentrated jet force at a point somewhat below the nozzle. At the same time a positive aspirating .force will be created, facilitating eifective entrainment of, pellets passing downwardly through channel 16 into the converging jets referred to. Thus, the multitudinous pellets supplied are forced by the jets so as to impinge on thcbottom of the bore hole, Again these pellets will be forced upwardly along the bore hole carried by the drilling fluid passing upwardly towards the surface of the ground. Opportunity is again provided for settling of the pellets from this drilling fluid in the enlarged cross-sectional area provided above the enlarged sleeve element l3. These pellets will therefore drop inwardly into the cup-shaped chamber provided by the sleeve element to be carried through channels 15' and thence through channel 16 for continued recirculation in the manner described.

in place of the plurality of nozzle passages 13 and jet nozzle 15, if desired, an annular nozzle passageway and an annular nozzle may be employed in the apparatus of Figure 2. In either case, an effective dead space is provided in which the pellets may be entrained in the fluid jet or jets. The desirability of rotating the drill of Figure 3 is again controlled by the factors identified in connection with the apparatus of Figure l. Directed drilling may also be obtained as formerly indicated.

In all embodiments of this invention, it is necessary to maintain the drill at a distance spaced from the bottom of the bore hole. Suitable placement of the drill in this manner may be maintained by a skilled operator by reference to the drilling rate maintained, as loss of drilling rate occurs when the jet is too close or too far from the bottom of the bore hole. However, it is preferred to employ positive means to space the jet nozzles at a desired distance vabove the bottom of the bore hole. For example, extensions may be positioned below the nozzles as illustrated by the downwardly extending rods 2%) in Figure 3. The extensions 20 are not provided with cutting terminations and will simply rest on the bottom of the bore hole bearing a small portion of the weight of the drill string. By this means the blunt extensions Ztl can permit an operator at the surface of the earth to feel the bottom in order to maintain the proper displacement of the jets from the bottom.

Another preferred arrangement for maintaining the fluid jet nozzle or nozzles a proper distance from the bottom of the bore hole is illustrated in Figures 5 and 6. In these drawings the apparatus illustrated is attached to. a drill string or other suitable tubing by means of the threads 30. in using the drill of Figure 5, rotation of the drill is required although the rotational rate may be slow and little rotational torque is required. Essentially the drill of Figure 5 consists of an eccentrically arranged stand-off provided with a supporting wheel. A primary jet nozzle 31 is provided through which fluid pumped through the drill string is ejected as a fluid jet. This fluid jet then passes through a secondary nozzle 32 which is arranged beneath the primary nozzle 31 so as to be concentric therewith. The internal diameter of the secondary nozzle is appreciably greater than the internal diameter of the primary nozzle.

Any desired arrangement may be employed to rotatably support a wheel 33 which is arranged to maintain the seconary nozzle 32 the optimum distance from the bottom of the bore hole. In the embodiment shown, the frame 34 to which the wheel 33 is connected is sufliciently massive to substantially block the portion of the bore hole to the right of the axis of the bore hole as illustrated. his limits the free path of drilling fluid circulation to the left half of the bore hole when the drill is in the position shown, so as to permit the differential velocity-gravity recirculation of pellets required.

in operating the drill ofFigure 5; as the bit is rotated, jetted fluid coming through the primary nozzle will entrain pellets, in part by an aspirating effect contributed by the enlarged diameter of the secondary nozzle 32. These pellets will attain some fraction of the velocity of the fluid jet inpassing through the secondary nozzle and will be ejected therefrom as a stream of high-kinetic-energy, directed pellets. When these pellets impinge on the bottom of the .bore hole a drilling action is achieved at the pattern indicated in the drawing. T.e pellets aaeaeoe Itl will be carried upwardly to be recirculated in the secondary nozzle in the general manner formerly described in connection with Figures 1 and 2. By rotating the drill as indicated, a helical cutting pattern is achieved by which progressively deeper drilling is obtained as the nozzles are rotated about the axis of the bore hole.

It should be observed that no appreciable weight need be placed on the stand-off arrangement described. It is only necessary to permit a sufficient portion of the weight of the drill pipe to be placed on the stand-oh" arrangement so that it will bear on the bottom of the bore hole at all times.

A desirable modification of the apparatus described concerns use of a guard deflector which protects the wheel bearing from random. impingement of the jetted pellets. A vertically extensive slot may be cut in the frame to accommodate a gate member, blocking the wheel hearing from the circulatory path of the jetted pellets. This is illustrated in Figure 5 wherein a plate element 36 is maintainedin aslot of the frame 34. The lower edge of the guard deflector 36 may be formed in accordance with the drilling pattern on which the deflector rests.

Dropping downwardly during drilling or forced downwardly by means such as spring 37, this deflector plate serves to protect the wheel bearing against wear due to random impingement of the jetted pellets. Forced downwardly by .gravity or by the spring means illustrated, a guard plate of the character indicated may effectively be used to limit the circulatory path of the pellets and to protect a stand-cit arrangement from wear by random impingement of pellets. A pin 39 maintained in frame 34 may be positioned in a slot iii of gate member 36 to hold the gate member within fixed limits of movement.

In the apparatus of Figure 5, as described, the fluid jets employed to propel the impact pellets are substantially aligned so as to be parallel to the axis of the bore hole midway between the wall of the bore hole and the axis of the bore hole. An alternative arrangement is illustrated in Figure 7, wherein the jet nozzles are maintained at an angle from the vertical or the axis of the bore hole. Thus in Figure 7 both the primary nozzle 31 and the secondary nozzle 32 are directed away from the axis of the bore hole and away from the bearing wheel 33 and the stand-off frame 34. In this embodiment of the invention the primary and secondary nozzles may be near the center of the bore hole although directed away from the center as described. This formof the invention has several advantages First,

by the non-vertical direction of the jets the normal rebounding path of the pellets impinging on the bottom of the bore hole is at angle to the direction of propulsion. Consequently, there is a tendency for the pellets to rebound in a path directed somewhat away from the ejection path of the secondary nozzles. This effect combines with the circulation effect of the drilling fluid so as to decrease the incidence of pellet to pellet contact. Again, the apparatus of Figure 7 serves to minimize wear of the stand-off frame due to contact of pellets therewith, since the pellets are directed away from the frame.

It is apparent that the apparatus described is uniquely adapted for prolonged periods of usage. As indicated, deterioration of the pellets which results in their washing from the bore hole with drill cuttings may readily be remedied by dropping additional pellets into the bore hole at the surface of the earth. The apparatus may bedesigned in the general manner described so that substantially no disabling wear occurs during normal drill- 12 little wear occurs. An outstanding advantage of the drill described, therefore, resides in the fact that extraordinarily long service life may be appreciated. The

necessity for removing the entire drill string from the scribed. Alternatively, a simplified form of equipment may be employed to provide the slow turning rates and low rotary torques which can be used. It is notable that little power is required to turn the freely suspended drill apparatus.

By virtue of the fact that the drill string is not rotated in the conventional manner, and need not be rotated at all, and by virtue of the fact that no appreciable weight is required on the drill bit at the bottom of the hole, substantially lighter drill strings may be employed. In this same connection failures of the drill string which are commonly caused by rotation under buckling forces due to ex ess weight stresses, may be substantially eliminated in this apparatus.

As described therefore, this invention concerns a novel drilling procedure in which a large number of spherical dense pellets are continuously circulated in the immediate vicinity of the bottom of a bore hole so as to secure repetitious impingement of these pellets against the bot tom of the bore hole. Continuous circulation of the pellets is maintained by a combination of gravity separain a sample of Bedt'ord Indiana limestone using a jet The.

pump of the general type described hereinbefore. limestone in this instance was a block 5 feet high. 7

Before each drilling operation was initiated, a small pilot or break-in hole Was first drilled into the surface of: the limestone to depths of about 12 to 18 inches using a' conventional 4% three-cone rotary drill bit. A cylindrical casing 5 inches I. D. and 7 feet long was placed on the block and centered over the pilot hole so as to form A pellet' impact jet pump bit assembly was then supported on the,

a drilling chamber simulating a bore hole.

end of a drill string within the casing.

The jet pump used in these experiments had a primary,

nozzle with a /8 inch I. D. and a secondary nozzle 15 inches long with a 1% inches I. D. The outlet of the primary nozzle was positioned 1 /3 inches above the entrance or top of the secondary nozzle to provide ample clearance for the entrance of pellets or other solid particles into the secondary nozzle.

The apparatus was further arranged and adapted so that drilling fluid could be pumped down through the drill string, out through the bit, and thence up to the annulus between the drill string and the wall of the bore hole to a mud pit or tank. Water was used as the drilling fluid in each test. 7

In each test, a 10 lb. charge of pellets or other particles was placed in the pilot hole; the drill assembly and surrounding casing were then placed over the pilot hole; the

lower edge of the casing was sealed against the face of the block; the slush pump was brought up to operating pressure; and the bit was lowered to a position about 5 inches above hole bottom. The bit was periodically ad-- In a first test, chunks of Bedford limestone having a .p. s. i. was supplied to the pump.

the invention. tube 5 inches I. D. was employed to simulate a bore hole,

maximum particle size of about inch were charged to the pump, and drilling fluid at a pressure of about 700 The flow rate of drilling fluid in this instance was maintained at a value sutfi cient to provide a fluid velocity within the bore hole annulus of about 124 feet per minute. It was observed in this test that all of the crushed limestone washed out of the bore hole within about 2 minutes of elapsed time,

and no measurable penetration of the underlying limestone block occurred.

In a second test, the apparatus was charged with inch diameter steel balls or pellets in place of the crushed limestone, the other operating conditions being maintained substantially identical with the first test. In this instance, none of the pellets were washed out of the bore hole, and an additional bore hole was formed to the extent of 19% inches.

In a third test, a charge of 24 mesh aluminum oxide abrasive was added to the drilling system in place of the limestone particles and the steel balls of the previous tests. The other operating conditions employed in this test were again substantially identical with the preceding tests. In this instance all of the abrasive material washed out of the bore hole, and no measurable amount of drilling was observed.

A fourth test was operated under substantially the same conditions as the previous three tests, with the exception that chilled steel shot inch in elfective diameter was charged to the drill bit in place of the crushed limestone, the steel balls and the aluminum oxide of the previous tests. In this instance all of the steel shot washed out of the bore hole within 3 minutes and no detectable degree of drilling could be observed.

It is apparent, then, from these tests that of the materials employed only the steel balls of the type falling within the scope of the present invention were effective in providing effective drilling. The crushed limestone particles, which essentially duplicate or simulate drill cuttings, were ineffective and were washed out of the bore hole within a very short period of time. The aluminum able characteristics and were ineffective in performing a satisfactory drilling operation.

In an effort to further determine whether drill cuttings in themselves could ever be satisfactorily employed for the purposes of this invention, an additional series of tests was run wherein it was determined what drilling fluid flow rate would be necessary to maintain the cuttings in the vicinity of a drill bit of the type embraced by In this series of tests a transparent Lucite and its lower end was closed ofli with a concave steel plug. The drill bit assembly placed within the tube was similar to that used in the above tests, and a lb. charge of inch crushed Bedford limestone was placed at the bottom of the hole. Drilling fluid in the form of Water was passed through the bit at various rates, and the bit was once again positioned such that the secondary nozzle was about 5 inches from the bottom of the hole.

By experimentation, it was found that a drilling fluid flow rate providing an annulus velocity of 119 feet per minute washed all of the limestone particles from the bore hole. It was further found that it was necessary to drop the flow rate to a value such that the drilling fluid velocity in the annulus was only 19.4 feet perminute before the particles could be satisfactorily recycled through the jet pump. It is apparent from these data that the use of drill cuttings in themselves are manifestly unsatisfactory for the purposes of the invention.

Another test was carried out with the apparatus just described wherein A inch steel shot was employed in place of the limestone particles. In this instance an annulus drilling fluid velocity of 98 feet per minute caused the shot to begin washing out of the bore hole; and a velocity of 1130 feet per minute found substantially all of the shot washed out of the hole. In the latter case none of the shot was recycled through the bit; and it is apparent, then, that steel pellets of a diameter smaller than that set forth in this invention cannot be satisfactorily employed for the purposes of the invention.

1 I claim:

1. An apparatus for drilling a bore hole in the earth in conjunction with a liquid drilling fluid which comprises in combination, a plurality of spherical steel pellets having a diameter of from about Vs to 1 inch, a tubular support member extending into the bore hole, a downwardly directed primary nozzle secured to said tubular support, an open ended tubular secondary nozzle supported from said tubular support and concentrically aligned with and extending below said primary nozzle, said secondary nozzle having an internal diameter at least about twice the diameter of the pellets, the upper end of said secondary nozzle being sufliciently spaced from said primary nozzle to define a passageway therebetween of a size sufficient to enable the pellets to pass therethrough, whereby said pellets are continuously recirculated through said secondary nozzle when said liquid drilling fluid is jetted through said primary and secondary nozzles from within said tubular support member.

2. An apparatus as defined in claim 1 in which the secondary nozzle has a length equal to at least about 10 internal diameters of the secondary nozzle.

3. An apparatus as defined in claim 1 in which the ratio of the diameter of the pellets to the inner diameter of the secondary nozzle is about 0.38/1.

4. An apparatus as defined in claim. 1 in which at least one extension member is attached to said apparatus and extends below the secondary nozzle a distance equivalent to about 2.4 to 3.8 secondary nozzle diameters.

5. An apparatus for drilling a bore hole through formations in the earth in conjunction with a liquid drilling fluid which comprises a jet pumphaving primary and secondary nozzles and adapted to be supported at the lower end of a string of well pipe, means for forcing the drilling fluid down through the well pipe and thence through the primary nozzle of the pump, the secondary nozzle of the pump being spaced from the primary nozzle to define a passageway therebetween large enough to pass drilling fluid and solid pellets, said pellets having a diameter within the range from about inch to 1 inch and a density greater than the earth formation and about 3 to 10 times the density of the drilling fluid, the secondary nozzle having a diameter at least twice that of the diameter of the pellets.

6. An apparatus as defined in claim 5 in which the secondary nozzle has a length equivalent to about at least 10 times its internal nozzle diameter.

7. An apparatus as defined in claim 5 including extension members secured to said pump and adapted to position the discharge end of the secondary nozzle about 2.4 to 3.8 secondary nozzle internal diameters distance from the bore hole bottom.

References Cited in the file of this patent UNITED STATES PATENTS 1,502,851 Gale July 29, 1924 2,072,627 Zublin Mar. 2, 1937 2,233,260 Hawthorne Feb. 25, 1941 

